[1]} is an improved version of CopyR [2]} model where they used a sequence tagging approach to extract multi-token entities. [3]} decomposed the joint extraction task into two sub-tasks: (i) head entity extraction (ii) tail entity and relation extraction. They used a sequence tagging approach to solve these two sub-tasks. Similarly, [4]} proposed a sequence tagging approach for this task. They first identified the head entities and then for each head entity and each relation, they identified the tail entities using a sequence tagging approach. They used pre-trained BERT [5]} in their model to improve the performance.
